Transformer Cooling Tubes

There are many electrical applications for thermography. Nearly every electrical apparatus in any type of facility is an excellent candidate for thermal inspection. One of the easiest, and often safest, types of electrical apparatus to inspect are oil-filled transformer cooling tubes.

Usually visual access to transformer cooling tubes is readily available. Often, inspection of transformer cooling tubes can be accomplished from well outside of clearance distances because they have such a large surface area. They’re usually several feet tall, and several inches wide, and since temperature measurement isn’t the goal of this type of inspection, IFOVmeas concerns don’t really apply.

Cooling tubes on oil-filled electrical devices, including transformers, operate on the simple principle of convective cooling. The oil is the cooling medium for the internal windings, and as it increases in temperature, it decreases in density as many fluid mediums do. The warmer oil is less dense and thus lighter than the surrounding cooler oil, so it tends to rise. As the oil cools it becomes denser and it tends to sink and natural circulation results.

In the image above, we can see four banks of cooling tubes on a transformer. The three banks on the left have what is considered a normal thermal pattern, while the one on the right has an abnormal pattern. Oil isn’t circulating in the right-hand bank of tubes. There are several potential root causes for this type of pattern, such as low oil, flow obstruction, a closed valve, or perhaps the apparatus is out of level.

When this type of condition exists, the cooling capacity of the device is negatively impacted. While in the cooler parts of the year, or when the device is lightly loaded, this might not be as great a concern. Whenever this type of pattern is detected however, it should be reported so it can be addressed before it becomes more critical.

There are many opportunities to apply infrared to electrical apparatus, transformer cooling tubes just be one. As a thermographer, look at the world around you with a thermal mindset and discover what you can see when you Think Thermally®.